Pyridyl cyanoguanidines such as pinacidil (N-1,2,2-trimethylpropyl-N′-cyano-N″-(4-pyridyl)guanidine) were originally discovered to be potassium channel openers and were consequently developed as antihypertensive agents. Replacement of the side chain of pinacidil by longer aryl-containing side chains caused a loss of the antihypertensive activity, but such compounds were, on the other hand, found to show antitumour activity on oral administration in a rat model carrying Yoshida ascites tumours.
Different classes of pyridyl cyanoguanidines with antiproliferative activity are disclosed in, for instance, EP 660 823, WO 98/54141, WO 98/54143, WO 98/54144, WO 98/54145, WO 00/61559 and WO 00/61561. The structure-activity relationships (SAR) of such compounds are discussed in C. Schou et al., Bioorganic and Medicinal Chemistry Letters 7(24), 1997, pp. 3095-3100, in which the antiproliferative effect of a number of pyridyl cyanoguanidines was tested in vitro on different human lung and breast cancer cell lines as well as on normal human fibroblasts.
P-J V Hjarnaa et al., Cancer Res. 59, 1999, pp. 5751-5757, report on the results of further testing of a specific cyanoguanidine compound, i.e. N-(6-(4-chlorophenoxy)hexyl)-N′-cyano-N″-(4-pyridyl)guanidine in in vitro and in vivo tests. The compound exhibited a potency in vitro which was comparable to that of the reference cytostatic agents daunorubicin and paclitaxel, while showing considerably less antiproliferative activity on normal human endothelial cells. In in vivo tests using nude mice transplanted with human tumour cells, the compound showed substantial antitumour activity, also against tumour cells that were resistant to conventional anticancer drugs such as paclitaxel.
A successful drug requires a subtle balance between factors such as activity, bio-availability, toxicity, level of side-affects, solubility, etc. which allows for improved cyanoguanidine based drugs.